Conventional devices for driving screws using a power tool such as a drill or the like are common in the art. These devices have a screwing head with a screw bit tip end which fits onto the head of a screw and a driveshaft end which is attached to the drive mechanism of the power tool. Recent advancements in screwing heads include devices with drive mechanisms which allow a screw to be counter-sunk at or below the surface of a workpiece. For example, the drive mechanism may include a clutch system in which a driveshaft is disengaged from the drive mechanism of the power tool to thereby stop the bit from turning when a desired counter-sinking depth is achieved. At the counter-sinking depth, the drive mechanism disengages from the screw bit thereby ceasing rotation of the screw bit, and likewise ceasing the turning of the screw. Examples of prior screwing heads include the devices of U.S. Pat. Nos. 4,287,923 and 4,753,142.
One disadvantage of prior screwing heads is that the radius of the screwing head proximate the screw driving bit is relatively large. A relatively large screwing head limits the number of degrees off normal the screwing head can be from the workpiece and still completely counter-sink the screw. Specifically, the suitable angle at which the screw can be driven into a workpiece, relative to the surface of the workpiece, is determined by the radius of the screw head, the radius of the screwing device proximate the bit tip, and the counter-sink depth. If the angle is too great, as the screw enters the workpiece at an angle, the drive mechanism of the screwing head will disengage from the screw bit, resulting in part of the head of the screw remaining above the surface of the workpiece, and therefore not counter-sunk into the workpiece. Although it is preferable to direct or drive screws into a workpiece at an angle normal (perpendicular) to the workpiece, often a screw is not perfectly normal and may be at an angle relative to the workpiece. With conventional screw driving heads, which have relatively large radii, e.g. 7.00 to 8.50 mm, the maximum angle at which the screw can be relative to the workpiece is typically less than 6.5 degrees off normal, i.e. 83.5 degrees relative to the workpiece surface. Since, the maximum angle between the screw and the workpiece surface in order to completely counter-sink a screw is determined by the radius of the screw head, the radius of the screwing driving device proximate the tip end and the counter-sink depth, the relatively large screw driving head radii of prior screwing heads limits the angle at which a screw can be driven and countersunk into a workpiece.
Accordingly, there is a need in the art for a screwing head which permits a screw to be at an angle greater than 6.5 degrees off of normal and still be able to counter-sink the screw into a workpiece.